This invention relates to the renovation of mains supply systems comprising supply pipes for the distribution of water, gas or fluids and has a particularly useful but not exclusive application to underground mains. Generally the systems comprise main delivery pipes, which are connected to the fluid supply, and a plurality of branchpipes or laterals which tap off the fluid supply to the final users.
A major problem arises when such underground pipes have deteriorated, for example through corrosion, ageing or other damage. Repairs by methods requiring the digging of trenches along the whole length of the pipeline disrupt road traffic, and potentially expose adjacent underground supplies by cable, pipe or other means to damage during the digging operations. These factors give rise to high maintenance costs for underground pipelines.
Various alternative methods are now being used to rehabilitate such existing mains, for example, by spraying materials which solidify as a lining in at least part of the existing pipe, thereby sealing leaks therein and prolonging the life of the mains pipes for many years. Other methods involve relining the pipes with plastics or rubber lining materials which may be bonded to the internal wall surface of the original pipe. Processes have also been proposed in which lining materials consisting of a textile tube coated with plastic materials are everted into pipes and bonded to the pipe walls by rigidifying epoxy resins. In these last-mentioned processes, it is necessary carefully to clean out debris from the pipe in order to ensure good adhesion between the lining and the original pipe. Furthermore, the reinforcement used must allow swell and dilation of the liner during insertion and eversion, in order that the liner can conform and adhere to the pipe wall surface, which requires that the liner itself be of fairly low bursting pressure. A further problem with this system is that the existing pipelines frequently have obtrusions in the wall, for example, where a redundant lateral pipe extends through the pipe wall, and these obtrusions frequently have sharp edges, which can cut through the liner when the system is pressurised with fluid during lining insertion or subsequent use. These necessitate careful cleaning and preparation of the internal surface of the pipe before inserting the new liner.